Familial X-linked hypophosphatemic rickets is inherited as an X-linked dominant genetic disease and is characterized by lifelong hypophosphatemia, increased renal phosphate clearance, normocalcemia, abnormal 1,25(OH)2D3 regulation and, in children, rickets resistant to vitamin D treatment. We are interested in studying the relationship between phosphate and calcitriol (an active form of vitamin D) treatment and parathyroid hormone secretion by analyzing their phosphorous, total calcium, ionized calcium,